1. The Field of the Invention
The present invention relates to systems and methods for monitoring a laser's wavelength and power. More particularly, the present invention relates to systems and methods for monitoring the wavelength and power of a laser by integrating the laser monitor with a transceiver.
2. Background and Relevant Art
Computer and data communications networks continue to develop and expand due to declining costs, improved performance of computer and networking equipment, the remarkable growth of the internet, and the resulting increased demand for communication bandwidth. Such increased demand is occurring both within and between metropolitan areas as well as within communications networks. These networks allow increased productivity and utilization of distributed computers or stations through the sharing of resources, the transfer of voice and data, and the processing of voice, data, and related information at the most efficient locations.
Moreover, as organizations have recognized the economic benefits of using communications networks, network applications such as electronic mail, voice and data transfer, host access, and shared and distributed databases are increasingly used as a means to increase user productivity. This increased demand, together with the growing number of distributed computing resources, has resulted in a rapid expansion of the number of fiber optic systems required.
Through fiber optics, digital data in the form of light signals is formed by light emitting diodes or lasers and then propagated through a fiber optic cable. Such light signals allow for high data transmission rates and high bandwidth capabilities. Other advantages of using light signals for data transmission include their resistance to electro-magnetic radiation that interferes with electrical signals; fiber optic cables' ability to prevent light signals from escaping, as can occur electrical signals in wire-based systems; and light, signals' ability to be transmitted over great distances without the signal loss typically associated with electrical signals on copper wire.
Wavelength Division Multiplexing (WDM) is a technique that increases the effective bandwidth of optical communications. The advantage of WDM systems is that multiple carrier wavelengths can be used to transmit data simultaneously as long as the carrier wavelengths do not interfere with each other. For example, channel spacing in the Dense Wavelength Division Multiplexing (DWDM) systems could range from 100 GHz down to 50 or 25 GHz.
Even though WDM is able to increase the effective bandwidth of optical communication systems, it is usually necessary to have precise control over the transmission or carrier wavelengths. The control over the carrier wavelengths is necessary in order to provide stable communication. Problems in WDM systems occur when the wavelengths begin to drift and thereby interfere with other carrier wavelengths. The need to monitor the carrier wavelengths becomes more important as the channel spacing becomes closer. Thus, monitoring the carrier wavelengths is particularly useful in DWDM rather than CWDM (Coarse WDM) systems.
Wavelength drift can occur for a variety of different reasons. Wavelength drift can occur, for example, when optical elements within a WDM system experience a temperature variation. This is particularly true with the laser, whose transmission wavelength is affected by temperature. The lasers of a WDM system are usually mounted to a thermo-electric cooler (TEC) that is designed to keep the laser at a fairly constant temperature. The wavelength generated by the laser can be controlled by adjusting the drive current and therefore the temperature of the TEC. The age of a particular laser also has an impact on wavelength drift. As a laser ages, the output wavelength changes.
Regardless of why the wavelength of a laser changes, it is necessary to ensure that the wavelength remains relatively constant during operation. To achieve this goal, WDM systems often implement an external feedback loop that is used to correct the wavelength being generated by the laser. In order to monitor the laser, a small portion of the laser output is siphoned off and sent to an optical element that can identify the wavelength of the laser light. The optical element is often referred to as a wavelength or channel monitor. The output of the wavelength monitor can be used to control the TEC, which controls the temperature of the laser and, ultimately, the wavelength of light emitted by the laser. The complete function is referred to as wavelength locking.
One of the problems associated with monitoring the transmission wavelength of a laser is that the optical elements needed to monitor the wavelength are not an integral part of an optical transceiver. Thus, a portion of the laser light must be isolated or siphoned off and fed, for example, to an external wavelength monitor.
Accordingly, there is a continuing need for improved methods and devices monitoring the wavelength and power of a laser.